Dihaloperfluoroalkanes, which may be represented by X(CF.sub.2).sub.n Y, where n is 1 to 7, are useful for making functional fluoromonomers and other useful organofluoromaterials. The diiodoperfluoroalkanes are also useful as chain transfer reagents for fluoroelastomers and in the free radical polymerization of fluorinated vinyl monomers. See for example U.S. Pat. Nos. 4,243,770 and 4,361,678, which are incorporated herein by reference.
CF.sub.2 I.sub.2 is a useful starting material for making organofluoromaterials and as a chain transfer agent for fluoroelastomers, but preparation methods have been shown to have low yields. The reaction of hexafluorocyclopropylene oxide (HFPO) with iodine in a stainless steel vessel has been reported (see John, E. O., et al., Inorg. Chem. 1992, 31, pp. 329-331) but the yield was reported to be 15-30%. Reaction of difluorocarbene with iodine gives less than a 20% yield of CF.sub.2 I.sub.2 as reported by Mitsh, R. A. J., Heterocyl. Chem. 1964, I, p. 233, and others.
SU-A- 1 297 411 teaches a preparation of difluorodibromomethane by reaction of bromine with hexafluoropropylene oxide, without catalyst.